The present invention relates to imaging apparatuses having an imaging element capable of reading out pixel signal of, for instance, an electronic still camera or a video camera and, more particularly, to imaging apparatuses having a so-called electronic shutter function of electrically controlling the exposure time.
As such an imaging apparatus, Japanese Patent Laid-Open No. 64-46379 discloses one, in which after the end of charge accumulation in the imaging element a read pulse for reading out the accumulated signal charge is generated at a predetermined timing, and in correspondence to this read pulse a sweep-out pulse for sweeping out the charge accumulated in the imaging element to the substrate and starting exposure, i.e., charge accumulation, afresh is generated at an instant in the vertical blanking period in a high shutter speed range and in a given horizontal blanking period in a low shutter speed range which is deviated from the vertical blanking period.
In this prior art imaging apparatus, in the high shutter speed range the timing of the sweep-out pulse generation is made variable within the vertical blanking period, thus permitting continuous shutter speed control. It is thus possible to control the exposure time such that the signal charge reaches an appropriate charge accumulation level at the instant of the read pulse generation and thus ensure high exposure accuracy.
However, in the low shutter speed range in which the sweep-out pulse generation timing is deviated from the vertical blanking period, the sweep-out pulse is generated fixedly in a given horizontal blanking period. Therefore, the shutter speed can be controlled only in time units of one horizontal sync signal, i.e., one horizontal line (1 H). For this reason, an error of 1 H at the most is generated in the actual exposure time, thus reducing the exposure accuracy. It is conceivable to make up for the excess and deficiency of signal charge from the appropriate charge accumulation level due to the exposure time error by controlling the gain of a following stage amplifier. In the amplifier gain control, however, the linearity is generally inferior. Therefore, this gain control does not permit accurate excess and deficiency correction. Besides, the S/N (signal-to-noise) ratio is varied with the gain.
The present invention was made in view of the above problems, and it has an object of providing an imaging apparatus capable of high accuracy control of the electronic shutter and ensuring high exposure accuracy.
According to an aspect of the present invention, there is provided an imaging apparatus having an imaging element for accumulating signal charge corresponding to an incident scene light flux in a photo-electric converting element section and capable of reading out the accumulated signal charge as a pixel signal comprising charge accumulation control means for controlling the instant of ending of charge accumulation in the imaging element to an instant other than the horizontal blanking period.
According to another aspect of the present invention, there is provided an imaging apparatus having an imaging element for accumulating signal charge corresponding to an incident scene light flux in a photo-electric converting element section and capable of reading out the accumulated signal charge as a pixel signal comprising charge accumulation control means for controlling the instant of ending of charge accumulation in the imaging element in time units shorter than the horizontal sync signal interval.
The following more specific structures are also provided:
The imaging element includes a charge accumulation area and a transfer shift register; and the charge accumulation control means ends charge accumulation in the imaging element by transferring signal charge accumulated in the charge accumulation area to the transfer shift register.
The imaging element includes a charge accumulation area; and the charge accumulation control means starts charge accumulation in the imaging element by sweeping out signal charge accumulated in the charge accumulation area to the substrate of the imaging element.
The imaging element is CCD.
The charge accumulation control means determines obtains an appropriate exposure time on the basis of the light measurement data of the subject scene image and determines the instant of ending of charge accumulation in the imaging element.
The exposure time control by the charge accumulation control of the charge accumulation control means is performed in 1 H unit.
The exposure time control by the charge accumulation control of the charge accumulation control means is performed in 1 V unit.
The imaging apparatus further comprising mechanical shutter for controlling the exposure time.
Other objects and features will be clarified from the following description with reference to attached drawings.